1. Technical Field
The present invention relates to a resonator element, a resonator, an electronic device and an electronic apparatus.
2. Related Art
In recent years, as a piezoelectric resonator element tends to be small, it is desirable that a CI (crystal impedance) value be decreased. It is known to adopt a mesa structure in order to decrease the CI value and confine vibration energy.
JP-A-2007-124441 discloses a piezoelectric resonator element that defines an optimum value of an etching amount from a substrate for obtaining a mesa structure. More specifically, in JP-A-2007-124441, when the etching amount is Md, a length of a long side of a quartz crystal substrate is x, and a thickness of a vibration section is t, if a percentage y of a ratio to the thickness of an etching amount Md of a step portion with reference to the thickness t is set, a relationship of y=−1.32×(x/t)+42.87 is satisfied. Therefore, it is disclosed that a minimum etching amount Md can be selected to allow a characteristic change in the CI value to be flat.
Further, JP-A-2008-263387 discloses that not only an optimum value of the etching amount from the substrate, but also a range of the length of the long side in an application range of conductive adhesive applied when the piezoelectric resonator element is mounted on a mount substrate are defined to suppress a binding of an unnecessary mode, and to promote a decrease in the IC value.
Furthermore, JP-A-2010-28610 discloses that a length from an end of a vibration section to an end of an excitation electrode is defined to suppress characteristic deterioration such as an increase in the CI value.
Therefore, the decrease in the CI value has been contemplated from various viewpoints.